The chemical analysis technique comprising partitioning a sample containing a sample component of interest from a liquid extractant with a membrane is known. The sample component of interest permeates through the membrane into the extractant which can then be analyzed to determine the component of interest. The specific membrane and extractant used are selected to enhance the extraction of the sample component of interest and to minimize or eliminate the extraction of other components of the sample that may not be of interest or that may interfere with the determination of the component of interest. One means used to determine a sample component of interest in the extractant is liquid chromatography and the overall system is then termed "membrane assisted liquid chromatography". In membrane assisted liquid chromatography a preselected volume of extractant containing the extracted sample component of interest is injected into a liquid chromatographic system and the sample component of interest is thereby determined.
One example of membrane assisted liquid chromatography is described in U.S. Pat. No. 4,529,521 to Hernan J. Cortes and James C. Davis. A sample of synthetic latex solution is partitioned from a water extractant by a bundle of dialysis type hollow fiber membranes. The water extractant is positioned in the bores of the hollow fibers and relatively low molecular weight components in the latex solution permeate through the membrane into the extractant. A syringe filled with water is used to pump the extractant from the bores of the hollow fibers into the injection loop of a liquid chromatography injection valve in the load position. A liquid chromatography pump is used to pump dilute sulfuric acid eluent through the injection valve, through a liquid chromatography column and then to a liquid chromatography photometric detector. When the injection valve is placed in the inject position, the eluent pumps the extractant in the injection loop onto the column and the extracted relatively low molecular weight components of the latex solution are chromatographed and eventually emerge from the column to be detected by the detector. If the latex sample is injected directly onto the column, the latex particles will soon plug the column.
The use of a membrane to pretreat a sample that can not be directly injected is a significant improvement in the art of liquid chromatography. However, at least one problem remains with this approach at its present state of development. This problem is the complexity of known membrane assisted liquid chromatography systems in that two solutions are used (extractant and eluent) and two pumping means are needed, one for the extractant and one for the eluent. The present invention is a solution to this problem.